1. Field of the Invention
Embodiments of the present invention generally relate to methods and apparatus for drilling and completing a well. More particularly, embodiments of the present invention relate to methods and apparatus for directionally drilling with casing. Even more particularly, embodiments of the present invention generally relate to the field of well drilling, particularly to the field of well drilling for the extraction of hydrocarbons from subsurface formations, wherein the direction of the drilling of the wellbore is steered and the need to determine the orientation of the drill bit within the earth is present.
2. Description of the Related Art
In conventional well completion operations, a wellbore is formed by drilling to access hydrocarbon-bearing formations. Drilling is accomplished utilizing a drill bit which is mounted on the end of a drill support member, commonly known as a drill string. The drill string is often rotated by a top drive or a rotary table on a surface platform or rig. Alternatively, the drill bit may be rotated by a downhole motor mounted at a lower end of the drill string. After drilling to a predetermined depth, the drill string and drill bit are removed (e.g., pulled out), and a section of the casing is lowered into the wellbore. An annular area is formed between the string of casing and the formation, and a cementing operation may then be conducted to fill the annular area with cement. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons.
It is common to employ more than one string of casing in a wellbore. Typically, the well is drilled to a first designated depth with a drill bit on a drill string. The drill string is then removed, and a first string of casing or conductor pipe is run into the wellbore and set in the drilled out portion of the wellbore. Cement is circulated into the annulus outside the casing string. Next, the well is drilled to a second designated depth, and a second string of casing or liner is run into the drilled out portion of the wellbore. The second string is set at a depth such that the upper portion of the second string of casing overlaps the lower portion of the first string of casing. The second liner string is fixed or hung off the first string of casing utilizing slips to wedge against an interior surface of the first casing. The second string of casing is then cemented. The process may be repeated with additional casing strings until the well has been drilled to a target depth. In this manner, wells are typically formed with two or more strings of casing of an ever-decreasing diameter.
As an alternative to the conventional method, a method of drilling with casing is often utilized to position casing strings of decreasing diameter within a wellbore. Drilling with casing utilizes a cutting structure (e.g., drill bit or drill shoe) attached to the lower end of the same casing string which will line the wellbore. The entire casing string may be rotated by mechanical devices at the surface, which ultimately rotates the drill bit so that the drill bit drills into the formation. Once the well has been drilled to the target depth with the casing in place, the casing may be cemented to complete the well. Additional casing strings may be run through the first casing string and drilled further into the formation to form a wellbore of a second depth, and this process may be completed with subsequent additional casing strings. Drilling with casing is often the preferred method of well completion because only one run-in of the working string into the wellbore is necessary to form and line the wellbore.
Drilling with casing is useful in drilling and lining a subsea wellbore, particularly in a deep water well completion operation. When forming a subsea wellbore, the length of wellbore that has been drilled with a drill string is subject to potential collapse because of the soft formations present at the ocean floor. Also, sections of the wellbore intersecting regions of high pressure can cause damage to the drilled wellbore during the time lapse between the formation of the wellbore and the lining of the wellbore. Drilling with casing removes such time lapses and alleviates these problems.
An alternative drilling with casing method which is sometimes practiced instead of rotating the casing string to drill into the formation involves “jetting” or pushing the casing into the formation. Because hydraulic energy from nozzles in a drill bit is often sufficient to remove the formation without using bit cutters, it is often necessary to jet the pipe into the ground by forcing pressurized fluid through the inner diameter of the casing string concurrent with lowering the casing string into the wellbore. The fluid and the mud are thus forced to flow upward outside the casing string, so that the casing string remains essentially hollow to receive the casing strings of decreasing diameter which contribute to lining the wellbore. To accomplish jetting of the pipe, holes or nozzles may be formed through the lower end of the drill bit to allow fluid flow through the casing string and up into the annular space between the outside of the casing string and the wellbore. The holes may be essentially symmetric with respect to the drill bit so that a uniform amount of fluid is released along the diameter of the casing string.
In a further alternate drilling with casing method, a motor and a drill bit may be attached to a drill pipe and positioned at a terminal portion of the first casing string to allow rotational drilling of the casing string into the formation if desired, as well as allowing jetting by lowering the casing string into the formation to continue. The drill bit may be rotated while the first casing string is lowered into the formation to facilitate drilling the first casing string to a desired depth. Upon reaching the desired depth, the drill bit and the drill pipe may continue to drill down to a target depth to enable placement of the second casing string. When casing string reaches the target depth, the drill pipe, motor, and drill bit are pulled out of the wellbore while the casing string remains within the wellbore prior to cementing the casing string into the wellbore. The second casing string is run in and placed in the wellbore at the target depth, the motor system retrieved, and then the second casing string is cemented therein. Additional cost and time for completing a wellbore are inherent results of the current drilling with casing operation because the motor system must be retrieved from the wellbore prior to the cementing operation.
For various reasons, it may be necessary to deviate from the natural (e.g., substantially vertical) direction of the wellbore and drill a deviated hole. Drilling with casing techniques may also be utilized to drill a deviated hole, commonly referred to as “directional drilling with casing.”
In subsea drilling operations, a drilling platform is supported by the subterranean formation at the bottom of a body of water. The drilling platform is the surface from which the casing sections and strings, cutting structures, and other supplies are lowered to form a subterranean wellbore lined with casing. Each drilling platform represents a relatively significant cost. Also, governmental regulations allow only a limited number of platforms over a given surface area of the body of water. Accordingly, platforms must be spaced a predetermined distance apart for drilling subterranean wellbores. Additionally, each platform must only occupy a specified area of the surface of the body of water. Because only a certain number of platforms of a given dimension are allowed over a given surface area and because of the possibly prohibitive economic cost of multiple platforms, the number of wellbores drilled into the subterranean formation should be the maximum amount of wellbores which can be drilled into the subterranean formation from the permitted platforms. In this manner, hydrocarbon production is maximized, because increasing the producing wells increases the hydrocarbons obtainable at the surface of the wellbore. Each wellbore formed is therefore valuable as an independent producing well which directly increases production from the hydrocarbon source.
A common problem with drilling subsea wellbores is encountered due to the attempt to maximize hydrocarbon production by maximizing the number of wellbores drilled from slots in a platform of limited surface area. To drill the maximum amount of wells, the slots in the platform must exist at extremely close proximity to one another. The closer the proximity of the slots to one another, the more wellbores which can be drilled over a given surface area. Unfortunately, drilling the wellbores through the slots which are so close to one another leaves little room for even small directional deviations when the wellbore is not drilled directly downward into the subsea formation. Sometimes, the wellbores are accidentally deflected and drilled into one another, causing the wellbores to intersect. When two or more wellbores intersect, at least one wellbore is eliminated as an independent hydrocarbon production source. Thus, the allowed drilling area from the platform is reduced, causing a decrease in the production of hydrocarbons from the subsea formation.
To avoid the intersection of wellbores, the wellbores are often drilled at an angle from the slots in the platform. The wellbores drilled from the outermost slots on the platform are typically drilled at an angle outward from the platform, and the outward angle decreases progressively for the inward slots. Thus, wellbores should deviate slightly away from other wellbores to avoid interference with one another. Other instances exist when it would be desirable to directionally drill a wellbore, such as when drilling at an angle is necessary to reach a production zone.
Various methods of deviated drilling or nudging are currently practiced. One method involves pre-drilling a hole directionally with a drill bit on a drill string. In this method, a wellbore is drilled into the formation at an angle. The drill string is then removed and a string of casing placed into the pre-drilled hole. This method fails to prevent caving in of the wellbore between the time in which the hole is drilled and the time in which the casing is inserted into the wellbore. Moreover, the increased time and expense inherent in running the drill string and the casing string into the wellbore separately are disadvantages of this method.
Another method to accomplish the deviation involves first drilling a pilot hole which is smaller in diameter than the desired wellbore and angled in the desired direction. The hole is then enlarged to subsequently run the casing therethrough. This method involves at least two run-ins of the drill string to drill two holes of different diameter, increasing time, expense, and wellbore collapse potential.
There is a need, therefore, for apparatus and methods which are effective for drilling the casing into the formation in subsea well completion operations. There is a further need for nudging methods and apparatus which effectively deviate the subterranean wellbore while drilling the string of casing into the formation to prevent intersection of the wellbores.
Additionally, with the current drilling systems, drilling tools and casing strings need to be run and/or retrieved a plurality of times into and/or out of the wellbore to complete drilling, casing, casing expansion, and cementing operations, resulting in substantial costs and length of time for completing a well. Therefore, there is a need for an apparatus and method for performing drilling, casing, expansion, and cementing operations which substantially reduce the time and costs for completing a well. Particularly, there is a need for an apparatus and method for performing a drilling operation while casing the wellbore which allows a cement operation to be performed subsequently without having to first retrieve the motor system utilized for the drilling operation. Additionally, it would be desirable for the apparatus to be able to perform these operations in a variety of settings utilizing different equipment and tools. It would be desirable for the apparatus to perform deviated drilling or nudging operations which produce deviated wells.
As an alternate technique of drilling with casing which may be utilized instead of merely attaching a cutting structure to the casing, a bottomhole assembly (“BHA”) having a drill bit may be lowered into the formation with a casing. The drill bit is exposed through the lower end of the casing, and the BHA is secured to a bottom portion of the inner diameter of the casing. After lowering the casing into the formation, the drill bit is rotated either in a rotary mode by rotating the casing (e.g., utilizing the casing as a drill string) or in a slide mode by rotating the bit independently of the casing with a downhole drill motor. In either case, as the wellbore is extended, additional lengths of casing are added to the wellbore from the surface as the casing string advances with the wellbore.
FIG. 32 illustrates a conventional system for directional drilling with casing using a BHA 3100. As illustrated, the BHA 3100 with a pilot drill bit 3108 is typically run through the casing 3104 (lining a wellbore 3102) and secured to a bottom portion of the casing 3104 with a casing latch 3106. As previously described, the BHA 3100 may be operated in a rotary mode, by rotating the casing from the surface of the wellbore. As an alternative, the BHA 3100 may include a downhole motor 3112 above the pilot bit 3108. As illustrated, the motor 3112 may be integral with a bent subassembly (or housing) 3114 to bias the pilot in the desired deviated direction (thus, the motor 3112 is commonly referred to as a “bent housing motor”). The deviated hole is drilled by adjusting the bent subassembly 3114 to point the pilot bit 3108 in the desired deviated direction. The trajectory of the deviated hole is typically dictated by the curvature that passes through the centers of the pilot bit 3108, the bend in the motor 3112, and the casing latch 3106.
The deviated wellbore must be larger than the outside diameter of the casing 3104 to allow the casing to advance as the wellbore is extended. This is typically accomplished by utilizing an underreamer 3110 to enlarge a pilot hole drilled with the pilot bit 3108. In other words, as the motor 3112 is operated, the pilot bit 3108 is rotated forming the pilot hole, which is then enlarged by the underreamer 3110 following behind. To run the BHA 3100 through the casing 3104, expandable blades of the underreamer 3110 may be placed in a retracted position. The blades may be expanded prior to drilling the deviated hole and again retracted to retrieve the BHA 3100, through the casing 3104, after drilling. The BHA 3100 may also include sensing equipment 3109, commonly referred to as a logging-while-drilling (LWD) or measuring-while-drilling (MWD), to take trajectory measurements (e.g., inclination and azimuth) and possibly formation measurements (e.g., resistivity, porosity, gamma, density, etc.) at several points along the wellbore which may be later used to approximate the wellbore path. MWD equipment usually contains the wellbore surveying sensors, while LWD equipment usually contains formation logging sensors.
The typical BHA 3100, when connected to the casing 3104 with the casing latch 3106, extends about 90 to 100 feet below the lower end of the casing 3104. The extension of the BHA 3100 below the casing 3104 allows the pilot drill bit 3108 to form a rat hole (extended wellbore) below the lower end of the casing 3104. The rat hole has a diameter larger than the outer diameter of the casing 3104 due to the underreamer 3110. In the typical directional drilling process utilizing the BHA 3100, the pilot bit 3108 is rotated to drill directionally the casing 3104 into a formation. The casing 3104 is then released from engagement with the casing latch 3106 of the BHA 3100, and the casing 3104 is lowered over the BHA 3100 to the bottom of the rat hole. The BHA 3100 is eventually removed from the wellbore, and the casing 3104 is left in the wellbore.
The rat hole formation step and the step of lowering the casing 3104 over the BHA 3100 are required when using the current system of drilling with casing 3104 using a BHA 3100 because the bent housing 3114 must have a bend extending below the casing 3104 sufficient to introduce the desired trajectory into the deviated hole. Thus, the directional force for drilling the directional wellbore is supplied by the motor 3112 bend of the bent housing 3114 of the BHA 3100, as the bent housing motor 3112 pushes directly on and against the side of the wellbore. Because the bent housing motor 3112 pushes against the side of the wellbore, a resultant force is caused on the opposite side, of the underreamer 3110 and pilot drill bit 3108.
While the system illustrated in FIG. 32 may allow for the drilling of a deviated wellbore without removing casing, the system suffers a number of disadvantages. As an example, one disadvantage arises due to a lack of proper support between the casing latch 3106 and the point of contact of the pilot bit 3108. As the typical length between the casing latch 3106 and the pilot bit 3108 may be in the range of between 40 feet to 120 feet, the BHA 3100 may buckle and lean towards a lower end of the deviated hole as downward force (i.e., “weight on bit”) is applied from the surface. This leaning is difficult to control and can severely affect the intended curvature and trajectory of the deviated hole. Further, without proper support, excessive lateral and axial vibrations in the BHA 3100 may reduce removal rate, reduce operating lifetime, and/or cause damage to the various components of the BHA 3110, particularly when drilling in rotary mode.
A further disadvantage of the system of FIG. 32 lies in the large length of the rat hole drilled below the lower end of the casing 3104, into which the casing 3104 must be lowered over the BHA 3100. Lowering the casing 3104 over the BHA 3100 in the 90-100 foot rat hole adds an extra step to the directional drilling with casing operation. Additionally, the system places unnecessary directional force directly on the BHA 3100. Still another disadvantage in conventional drilling with casing systems is that the MWD 3109 does not provide real time survey information and, thus, the trajectory of the deviated hole can only be verified after drilling. This is unfortunate because real time feedback regarding the trajectory of the wellbore as it is being extended could be used to control the drilling process (e.g., adjust rotation speed of the bit, weight-on-bit, steer a rotary-steerable assembly or downhole motor, etc.), to control the trajectory of the wellbore.
When directionally drilling with a drill string, as the well is drilled, the bore direction must be checked or monitored, to ensure that the bore direction is not deviating from its intended direction. Such monitoring is typically provided by positioning a survey tool in a downhole location, in a rotationally fixed or known position, and monitoring signals therefrom to determine the orientation of the drill string in the earth. Where the drill string is pulled from the well after the wellbore is drilled, and the well is then cased, this is easily accomplished by fixing the survey tool in a subassembly in the drill string, and thus the survey tool is continuously in the borehole when the drill bit is at the bottom of the hole. However, where the drill string is later used as the casing, this is not practicable because the orientation tool is expensive, and therefore it is undesirable to abandon it in the well. Also, the survey tool, if left in the well, would create an obstruction to well fluid recovery, or for the passage of an additional drilling element therepast and thence through the end of the casing to continue drilling the borehole to greater extent, and thus would need to be drilled or milled out of the bore hole. Therefore, there exists a need in the art for a mechanism to provide downhole orientation tools in situations where the drill string is subsequently used, in situ, as the well casing, without creating an undue impediment to well fluid recovery, and without the economic consequences of leaving the survey tool in the hole after the well is complete.